The invention concerns a snugly fitting denture such as bridges and the like, consisting of a metallic foundation and a ceramic facing shell, which is silanized and fixed to the foundation by means of cold-polymeride, as well as a process for its manufacture.
Denture materials which have stood the test of time are plastic (mostly derivatives of polymethyl methacrylate) alloys (noble metals and other alloys of base metals being resistant to the conditions prevailing in the oral cavity) and ceramic materials. Most of these aids to therapy are built up from several materials and their clinical usefulnss is determined to a decisive extent by their compactness.
While the homologous joining of materials (metal to metal, plastic to plastic, ceramic to ceramic) is largely without problems during processing in the dental laboratory, heterogeneous combinations of materials may lead to difficulties if its adherence should surpass the firmness of pure mechanical retention. In this context the joining of metal to ceramic (e.g. DE-OS 2 106 013) and the joining of plastic to ceramic according to DD-WP 148 857 could be considered as being solved during the last decades. According to which a mineral tooth with silane coupled adhesive plastic part is proposed in which the basic materials of the individual layers of the mineral tooth have grain sizes in a fractionation from less than 60 .mu.m to 100 .mu.m. The adhesive plastic part applied to the silane layer consisting of a multicomponent mixture made of polymethacrylic acid methylester, dioxane, methacrylic acid methylester, a sensitizer and a vapour pressure reducer are arranged in the dorsal and basal areas respectively of the mineral tooth. The mineral tooth is immersed several times into the silane solution and dried subsequently and thereafter the multicomponent mixture is applied to the dorsal and basal areas respectively of the presilanized mineral tooth without any pressure using a source of heat radiation with temperatures between 20.degree. and 50.degree. C. and during a period of time between 3 and 6 minutes and is polymerized without pressure. Heretofore the results of attempts to join plastic with metals in a slitless manner are not satisfactory. This combination of materials is of particular importance with toothcoloured facing of metallic materials within the frame of the technique using crowns and bridges (firmly fitting dentures). Here defective joining will lead to premature separation of the facing, formation of marginal slits with exogenous discolouring of the plastic (due to oxidation of the metal scaffolding and seeping-in of colouring substances), restricted biocompatibility due to mechanical irritation of tissue at the slit between facing and scaffolding, formation of plaques and increased bacterial settlement.
The prerequisites of the firmess of the joining depend on the load imposed by clinical use. To these belong predominantly physical-mechanical loads, influences due to saliva, foodstuffs, drugs, microbes and changing temperatures. Factors influencing adherence on the part of materials are polymerization of plastic, shrinking due to polymerization, differences in temperature and density, time, viscosity of processing, elastic properties of plastic and pretreatment of adhesive areas.
Until now the problem of adherence of metal to plastic under the conditions of the oral cavity is still unsolved. Using the known compounds, mechanical anchoring and at best adhesion may be anticipated. In order to prevent separation of plastics, which were polymerized onto metals, space-occupying and indication restricting retentions with sites extending under themselves are necessary. Thus separation may be prevented in general, but not the formation of slits. According to publication DE-OS 2 162 608 an agent is known, which serves for covering of metal scaffoldings and of butt metal for plastic facings for dental prosthetics consisting in essentially of a mixed polymeride from about 20 to 60 parts w/w acrylonitrile and 40 to 60 parts w/w of methylmethacrylate. In addition the mixed polymeride contains up to 5 parts w/w of methacrylic acid as well as 0.01 to 1 part w/w of a silicon hydrogen compound for improving adherence. The process for opaquization of the metal foundation for crowns and bridge-prosthesis is characterized by the fact, that the mixed polymeride is dissolved in a solvent consisting of nitroparaffins and/or halogenated hydrocarbons, an opaquization pigment is dispersed in this solvent as well as an adhesion improving agent .gamma.-methacryloxipropyl trimethoxysilane and the resulting agent is applied to the surface of a dental metal alloy foundation, of a noble-metal or of a noble-metal alloy. When the solvent has escaped a dental resin for crowns or bridges is applied in a methyl methacrylate monomer-carrier at the opaquized surface for the manufacture of dental products.
Due to the good results, which were obtained with the use of silanes as mediator of adherence, it was proposed for the manufacture of crowns and bridges the basic scaffoldings of which consist of metallic materials to use prefabricated mineral facets, which are silanized and are fixed by means of a cold polymeride to the metallic bridge scaffolding. Adherence of hot polymerized plastics is particularly poor because of additional tensions due to shrinking, because of cooling down, although this plastic material is distinguished by improved durability under the conditions prevailing in the oral cavity. Pressure-heat-polymerization which was recommended recently also diminishes the size of the slits only, but does not prevent them.
Better is the firmness of joining of cold plastics, which occasionally develop a certain adhesive power. The more thin the applied layers of plastic the lesser are the tensions depending on shrinking due to polymerization. However cold plastics also show a considerable drop in adhesive properties after storage in water under the conditions prevailing within the oral cavity.
Adhesive lacquers and coating lacquers which were recommended in order to improve adhesive strength and reduction in slit formation, have not proven to be satisfactory. Silanes applied in a thin layer onto the metal as so-called primers have also been recommended, but until now have not found general introduction.
The aim of the invention is to avoid the disadvantages of the solutions known until now and to provide for a snugly fitting denture, which while fulfilling high aesthetic demands may be manufactured in dental laboratories with a small economic expenditure.